Bacterial survival in soil is affected by moisture content, temperature, organic matter, and antagonism by soil microflora. In most instances the survival of bacterial pathogens in the soil is less than 2-3 months. Removal of bacteria from sewage during percolation through the soil is accomplished largely at the soil surface by straining, sedimentation, and adsorption. While relatively large numbers of bacteria and viruses appear to be removed through a few feet of soil under normal conditions, once they have gained entrance into the underground aquifer distances of travel as far as several hundred feet have been observed. Removal of viruses by soil occurs largely by adsorption. Salt concentration, pH, soil composition, organic matter, and the electronegativity of the virus and the soil may influence the degree of retention of viruses by the soil. Viruses attached to soil particles can become deadsorbed with changes in water quality, resulting in greater subsurface travel. Viruses survive at least as long as pathogenic bacteria in the soil.